This invention was the subject matter of Document Disclosure Program Registration numbers 310281, 312808 and 313901 which were filed in the United States Patent and Trademark Office on May 22, 1992, Jul. 8, 1992 and Jul. 23, 1992 respectively.
The use of radars in collision avoidance systems is generally known. U.S. Pat. No. 4,403,220 dated Sep. 6, 1983 discloses a radar system adapted to detect relative headings between aircraft or ships at sea and a detected object moving relative to the ground. The system is adapted to collision avoidance application. U.S. Pat. No. 4,072,945 dated Feb. 7, 1978 discloses a radar-operated collision avoidance system for roadway vehicles. The system senses the vehicle speed relative to an object and its distance and decides whether the vehicle is approaching the object at a dangerously high speed. A minimum allowable distance represented by a digital code is stored in a memory of a computer and the minimum allowable distance is compared with the distance sensed by the radar. U.S Pat. No. 4,626,850 dated Dec. 2, 1986 discloses a dual operational mode vehicle detection and collision avoidance apparatus using a single active or passive ultrasonic ranging device. The system is particularly adapted to scan the rear and the lateral sides of the motor vehicle to warn the vehicle user of any danger when changing lanes.
Most of the prior art collision avoidance systems use microwave radars as the ranging and detecting device. There are multiple disadvantages of these automobile collision avoidance systems when microwave radars are used. One major disadvantage is related to the beam width, that is the angular width of the main lobe of the radar, and the associated angular resolution of the microwave radar. The beam width is inversely proportional to the antenna diameter in wavelength. With the limitation of the antenna size, it is very difficult to make a reasonable size microwave radar with beam width less than 3 degrees. At the desired scanning distance, this beam width will scan an area which is much too big and thus is too nonspecific and difficult to differentiate the received echoes. Besides getting echo from another car in front of it, this radar will also receive echoes from roadside signs, trees or posts, or bridges overpassing an expressway. On highways with divided lanes the microwave radar will receive echoes from cars 2 or 3 lanes away and has difficulty to indifferentiating them from echoes coming from objects in the same lane. Because of the poor angular resolution of microwave radars, the direction of objects can not be specifically determined and objects too close to one another cannot be separated. The angular resolution of microwave radars is not small enough for them to be effectively used to monitor roadway traffic. The other disadvantage is that the microwave radars have difficulty in distinguishing radar signals coming from adjacent cars with similar equipment. If there are more than two cars with the same radar equipment on the same scene, the signals become very confusing.
The ultrasonic ranging and detecting device's angular resolution is also too poor to be effectively used in roadway traffic monitoring. The ultrasonic devices have even more difficulty than the microwave radars in determining the direction and location of echoes precisely, in the detection of directional change of objects and in avoiding signals coming from adjacent vehicles with similar equipment.
In the first, second and third preferred embodiments of this invention, laser radars are used in automobile collision avoidance systems to avoid the above disadvantages of microwave radars or ultrasonic devices.
In the prior art, there is no accurate way to predict when a collision may happen when dealing with a mobile obstacle, especially when the obstacle is moving in a direction different from the direction of the system-equipped vehicle. It is very important to be able to precisely predict a collision in order to give a proper warning as soon as possible and, meanwhile to avoid unnecessary warnings. In the first, second and third embodiments of this invention, novel ways to more precisely predict collisions are disclosed.
In U.S. Pat. No. 4,072,945 dated Feb. 7, 1978 Katsumata et al uses minimum allowable distance as the basis for their collision avoidance system. However, the concept of minimum allowable distance fails to take into consideration many other factors which influence the collision timing. In this invention a novel concept of minimum allowable time is disclosed. Minimum allowable time can be easily adjusted by other factors, including road condition, visibility, driver's physical and mental condition and other factors.
Furthermore, in the prior art there is no reliable way to get information from the system-equipped vehicle's directional change. In the third embodiment of this invention, a novel concept of utilizing a laser gyroscope to get very accurate information of directional change of the system-equipped vehicle is disclosed.
Wheel skidding is another important cause of vehicle collisions or accidents. The prior art is replete in roadway vehicles with four wheel steering capability with various designs to control the steering of rear wheels. It has been well known that steering the front wheels and rear wheels in the same direction also called coincidence-phase direction, at a high vehicle speed can promote the stability of the vehicle and decrease the possible lateral skidding of wheels caused by the centrifugal force during turning. Adjusting the rear wheel steering angle is used to prevent or correct wheel skidding.
U.S Pat. No. 5,103,925 dated Apr. 14, 1992 includes a rotational speed sensor for each wheel, wherein detection of difference in rotational speed between the front and rear wheels indicates presence of wheel skidding during turning. When wheel skidding is detected, a correction value is applied to modify the rear wheel steered angle. However, using the difference in rotating speed between the front wheels and the rear wheels as a basis for detecting wheel skidding will become inaccurate when wheel skidding occurs on wet roads or icy roads or when there is wheel locking due to excessive brake application. In the fourth embodiment of this invention a new and improved wheel skidding detecting system based on a laser gyroscope will be disclosed.